1. Field of the Invention
The invention relates to the exhaust gas turbine of an exhaust gas turbocharger which is connected to an internal combustion engine.
2. Discussion of Background
During operation of an exhaust gas turbocharger, the exhaust gas turbine of the latter is exposed to relatively high temperatures from the internal combustion engine connected thereto. High thermal stresses thus arise in the turbine-side components, such as for example the gas inlet casing, the nozzle ring, the covering ring and the gas outlet casing. Since each of these components is at a different distance from the internal combustion engine and, moreover, different materials are used, the component temperatures differ accordingly. This results in different thermal expansions with relative movements between the individual components, which may lead to screws breaking, gas leakages and components cracking. The design and arrangement of the separating locations of gas inlet casing, gas outlet casing, nozzle ring and covering ring thus play an important part in the ability of an exhaust gas turbocharger to function.
DE-A1-4223496 has disclosed a screw connection of the nozzle ring to the gas inlet casing. For this connection, the inner ring of the nozzle ring is of thickened design and provided with an additional flange which receives the screws serving for connection to the gas inlet casing.
The one-sided screw connection may lead to irreversible distortions of the nozzle ring in the event of such a solution. Moreover, there is the risk of a bypass flow being formed on the outer ring of the nozzle ring, as a result of which the efficiency of the exhaust gas turbine and thus that of the turbocharger is reduced. Owing to the high generation of heat on the turbine side, the screws serving to fasten the nozzle ring are positioned in a very fixed manner and can only be removed with very great difficulty. The assembly time required to exchange the nozzle ring is therefore considerably lengthened, which is a significant disadvantage for the internal combustion engine which is connected to the exhaust gas turbocharger and is dependent on the latter in terms of its power.
EP-B1-191380 shows the exhaust gas turbine of an exhaust gas turbocharger, the nozzle ring of which turbine is clamped against the gas inlet casing by the covering ring. For this purpose, the outer ring of the nozzle ring has an axial projection and the covering ring has a corresponding fastening flange. The latter is connected to the gas inlet casing by means of a plurality of screws. In the peripheral direction, the nozzle ring is fixed on the gas inlet casing by means of positively locking centering bolts.
A drawback which is common to both solutions is that the nozzle ring in each case has an additional component for arranging or accommodating fastening elements. As a result, its production is complicated and thus relatively expensive. Moreover, both the axial projection of the outer ring and the flange of the inner ring are at risk from cracking, owing to the thermal stresses which have already been described above, as a result of which reliable fastening of the nozzle ring and thus the functioning of the turbocharger are not ensured in the long term.